CONTROL OF BLACK SPOT OF PEAR.

New Zealand Journal of Agriculture, Volume XVIII, Issue 4, 21 April 1919, Page 221

CONTROL OF BLACK SPOT OF PEAR.

SPRAYING-TESTS AT TE KAUWHATA.

By

L. PAYNTER,

Orchard Instructor, Hamilton

In view of the diversity of opinion regarding the control of blackspot of pear (Fusicladium pyrinum) . in the Auckland Province it was arranged by the Horticulture Division to take over a portion of Mr. J. B. Haxton’s pear-orchard at Te Kauwhata, with The object of ascertaining whether or not it was possible to effectually control this disease under the adverse conditions often prevailing there. The failure of growers to control black-spot has been very apparent for some years past. The Fruit Inspectors in charge of the large centres have had a considerable quantity of fruit to condemn for this trouble. In this state of affairs it was considered the best course to try and convince growers that the fault in the main lay with themselves, in the shape of defective spraying. Whether the object has been accomplished may be left to readers of the following record to judge. Taking all the facts into consideration, and in conjunction with the results obtained in orchards in close proximity to the area under review, I think the percentage secured of clean fruit shows plainly that it is quite possible to reduce the infection to a minimum. The season just past will be admitted by most, if not all, to have been one in which the development of the spores of. black-spot has been very rapid, necessitating constant spraying to prevent infection. The area selected consisted • of - Williams Bon Chretien pears, and was divided into four equal plots, each containing eighty-four trees, this being not so much with the idea of testing various sprayingcompounds, ' but to ascertain, if possible, the minimum amount of spraying necessary if satisfactory work is to be accomplished.

Previous to the. application of lime-sulphur to plots i and 2, on 27th August, the weather had been very wet. Plots 2 and 3 'were sprayed on 1st October, as per table. This was intended as a cluster-bud spray, but owing to weather conditions the application was delayed , nearly a week. . Immediately after this rain set in again, but continued only for a few hours, followed afterwards by a

week of sunshine. At the time the next spraying was to be done rain again fell and continued for a few days, thus delaying what I consider the most important application —namely, 6-4-50 Bordeaux at the pink stage. The weather being warm at this time;10th October —many of the trees were showing a great deal of bloom.- It was a bright , day when this application was given. Rain set in again the next day and continued almost every day up to the 31st, when the next application was given, it being also a bright day. Rain fell again the next day, and continued for a few days, making conditions favourable for the development of black-spot. Following upon this there came a spell of fine weather and warm days. The next application was given on 25th November, as per table, and was no sooner completed than light misty rain commenced to fall, but lasted only a few hours. The days intervening between this and the . next application, . on 17th December, were more or less showery. There was only one day . in which no rain fell. After the last-mentioned application the weather was fairly fine until the New Year, when rain again set in, making conditions exceptionally favourable for the development and spread of the fungus-spores. The last application was given on 7th January, as per table. I may add that with the last four sprayings, commencing on 31st October, arsenate of lead was added for the control of codlin-motln The results were as follows:—•

Although the. results are not quite up to expectations, consideration must- be given to the fact that the writer’s headquarters are thirty-five miles from the test area. This inconvenience the orchardist does not have to face, as he is always on the scene of action and in a better position to watch developments, and should therefore get even better results. I feel confident that as the percentage of infection during a bad season and under such conditions as mentioned was brought to the point just recorded there should be little or no trouble in reducing the infection even lower.

The foregoing data show the least infection upon the plots that received the cluster-bud spray in addition to the pink spray. This must be considered in conjunction with the weather conditions prevailing at the time of application.

The cluster-bud spraying was delayed almost long enough to call it the pink spray, as a great many of the buds were at that time showing pink. Moreover, when the pink spray was applied many of the trees were almost in full bloom. This was particularly so with plot No. 1.

The greater portion of the remainder of Mr. Haxton’s orchard was in a very bad state, and would show at least 50 per cent, of black-spot infection, if not more.

The question of cost has been raised in considering the amount .of spraying given to the plots under test. This has not been lost, sight of. The material used, also time taken to-carry out the work, are as follows Bluestone (130 lb.), £5 ; lime (three tins), 15s. ; lime-sulphur (8 gallons), £1 12s. 3 time (five days), £3 15s. : total, fix 2s. This works out at about 8d. per tree, which is not a very great item. It must also be remembered that the above is the maximum. of spraying required. If weather conditions were favourable it could be reduced probably to about half, but “better sure than sorry.” It is worth noting here that the crop of pears this season was light. The cost of spraying a heavy crop would be very little more.In conclusion I may state that nothing less than thorough application of the sprays is of any use. It is quite necessary for a covering of the fungicide to be kept on the fruit to prevent infection, and more especially when conditions are such as to favour the development and spread of such a disease as black-spot.

. Plot No. . Spray. Date'of Spraying. . Date of Spraying. i and 2 . . . Lime-sulphur, 1-12 . . . . . . -■ 27th August. 2 and 3 Bordeaux mixture, 8—6—40 ... 1st October. i, 2, 3, and 4 . . Bordeaux mixture, 6—4—50 . . 10th October. 1, 2, 3, and 4 . . Bordeaux mixture, 3—4—40 . . . . 31st October. 1, 2, 3, and 4 . . Bordeaux mixture, 3—4—40 . . ' 25th November 1, 2, 3, and 4 . . Bordeaux mixture, 3-4-40 . . . . 17th December. 1, 2, 3, and 4 . . Bordeaux mixture, 3-4-40 7th January.

The plots were sprayed as follows

Plot No. . Total Crop. Infected Fruit. Percentage of infection. Cases. ■ ■ Cases. I 99 4 14 2 137 -5i 4' . 3 IOI - 5i 5i . 4 6i 8 13 Grand total 398 33 Average 8|-